This is another common interview question, but appropriate for primary school. You have 8 balls which look identical. 7 of them have the same weight, while 1 is heavier. How can you find the heavier ball by using a balance with only 2 weighings? The most common way (but this will require 3 weighings) would[…]

This is apparently a common interview question: In a bid to have more boys, every family in a certain country will continue to try for children until they have a boy. If they have a girl, they’ll keep trying. If they have one boy, they’ll stop. What will be the proportion of girls to boys[…]